We propose to continue our investigations into the manner by which hallucinogenic drugs produce changes in sensory, associative and motor processes. The main procedures to be used will involve the classical (Pavlovian) conditioning paradigm whose essential feature is a set of experimental operations involving an aversive or appetitive unconditioned stimulus (UCS), which reliably produces a measureable unconditioned response (UCR), and a conditioned stimulus (CS) that has been shown by empirical tests not to initially produce a response resembling the UCR. The CS and UCS are then presented repeatedly to the organism in a specified order and temporal spacing, and a response similar to the UCR develops to the CS that is called the conditioned response (CR). The analytical power of this paradigm is the ability to exactly specify the stimulus conditions governing acquisition, as well as other aspects of learned behavior (i.e., extinction, retention, differentiation, etc.) and to delineate the associative effects of the variables of interest from their effects on nonassociative, sensory and motor processes. Accordingly, we are interested in comparing the effects of LSD and other hallucinogens (Psilocin, DMT, DOM and mescaline) on acquisition in classical defense (rabbit nictitating membrane) and classical reward (rabbit jaw movement) conditioning in order to determine a common effect of hallucinogens on such acquisition processes that is not shared by inactive compounds such as BOL, bufotenine or amphetamine. We will also examine drug effects on extinction, CS induced excitability on UCRs, sensory processing (as measured in differential conditioning, pattern discrimination and conditioned inhibition) and motor processes through examination of UCRs. Furthermore, we will examine the occurrence of tolerance and cross-tolerance between the various hallucinogenic agents on these behavioral indices and examine the ability of procedures that increase or decrease monoamine content of brain to enhance or block the actions of hallucinogenic drugs or alter the development of tolerance.